James J. Guregian

Bio: James J. Guregian is an academic researcher. The author has contributed to research in topics: Space Shuttle & Telescope. The author has an hindex of 2, co-authored 2 publications receiving 15 citations.

Overview of contamination effects on the performance of high-straylight-rejection telescopes via ground measurements

Abstract: The contamination control of telescopes with the straylight-rejection capability is reviewed to identify the degradative effects of contaminant phenomena on the measurements. Three levels of optical contamination are discussed including bidirectional reflectance distribution function (BRDF), point-source rejection ratio (PSRR), and nonrejected earth radiance (NRER). Measurements of degradation to low-scatter surfaces are set forth for the Zip telescope during storage and for the Cirris 1A telescope performance. PSRR measurements indicate that the Cirris 1A degraded by a factor of 15 during ground testing. A portable external BRDF station is described that measured cryogenic BRDF and BRDF degradation over the life of the Cirris 1A telescope. The optical contamination measurement described are concluded to be important to both determining the causes of degradation and optimizing telescope performance.

An assessment of the near-field contamination and off-axis leakage effects on earthlimb background measurements from CIRRIS 1A

Abstract: Efforts to reduce or eliminate contamination and off-axis leakage for the Cryogenic Infrared Radiance Instrument for the Shuttle (CIRRIS) 1A program flown on STS-39 are examined. The question of whether the Space Shuttle is a viable platform for space measurements is addressed. Mission restrictions and system precautions are reviewed. Results obtained are compared to the current models and previous data. The data show how telescope leakage and/or contamination effects can dominate the minimum signal floor and place a limit on the weakest signal that can be measured when these undesired elements are present. The Space Shuttle is found to be an acceptable platform for high-sensitivity earthlimb background and celestial measurements if prudent clean procedures are followed. Acceptable mirror bidirection reflectance distribution function can be monitored over a considerable period of time if the sensor has been pumped for a considerable period of time and careful handling procedures are followed.

Contamination control engineering design guidelines for the aerospace community

Abstract: Thermal control surfaces, solar arrays, and optical devices may be adversely affected by a small quantity of molecular and/or particulate contamination. What is rarely discussed is how one: (1) quantifies the level of contamination that must be maintained in order for the system to function properly, and (2) enforces contamination control to ensure compliance with requirements. This document is designed to address these specific issues and is intended to serve as a handbook on contamination control for the reader, illustrating process and methodology while providing direction to more detailed references when needed. The effects of molecular contamination on reflecting and transmitting surfaces are examined and quantified in accordance with MIL STD 1246C. The generation, transportation, and deposition of molecular contamination is reviewed and specific examples are worked to illustrate the process a design engineer can use to estimate end of life cleanliness levels required by solar arrays, thermal control surfaces, and optical surfaces. A similar process is used to describe the effect of particulate contamination as related to percent area coverage (PAC) and bi-directional reflectance distribution function (BRDF). Relationships between PAC and surface cleanliness, which include the effects of submicron sized particles, are developed and BRDF is related to specific sensor design parameters such as Point Source Transmittance (PST). The pros and cons of various methods of preventing, monitoring, and cleaning surfaces are examined and discussed.

History of Space-Based Infrared Astronomy and the Air Force Infrared Celestial Backgrounds Program

Abstract: : A retrospective is provided on space-based astronomy missions and the prominent role the US Defense Department (DoD), particularly the Air Force, played in early days of infrared astronomy and the technology development that was transitioned to the infrared astronomical community The geophysics programs at the Air Force Cambridge Research Laboratories (AFCRL) and successor organizations (AFGL) at Hanscom Air Force Base are described in order to provide a context for the DoD infrared astronomy program AFCRL and AFGL conducted the early mid-infrared probe-rocket based surveys as well as supporting related experiments under university contracts The succession of subsequent orbital experiments is also described

Space shuttle observations of collisionally excited outgassed water vapor

Abstract: The analysis of CIRRIS 1A (Cryogenic InfraRed Radiance Instrumentation for Shuttle) interferometric and radiometric data obtained during the flight of STS-39 (28 Apr–6 May 1991) reveals the presence of IR emission in the 400–900 cm−1 (11–25 μm) region not attributable to atmospheric emission. In this paper, data are shown which identify the signal as near-field water vapor present during all CIRRIS 1A observations. Variability of the near-field water vapor emissions is characterized, and further investigation indicates that the water is excited to high effective temperatures, possibly in excess of 2000 K. The data presented support the conclusion that water outgassed from the shuttle tiles is highly excited by collisions with atmospheric O, classifying it as a type of shuttle-induced glow whose spectrum has never previously been measured in the LWIR. Measured results are compared to current models which predict radiance for collisionally excited outgassed molecules.

Infrared Sky Surveys

Abstract: A retrospective is given on infrared sky surveys from Thomas Edison’s proposal in the late 1870s to IRAS, the first sensitive mid- to far-infrared all-sky survey, and the mid-1990s experiments that filled in the IRAS deficiencies. The emerging technology for space-based surveys is highlighted, as is the prominent role the US Defense Department, particularly the Air Force, played in developing and applying detector and cryogenic sensor advances to early mid-infrared probe-rocket and satellite-based surveys. This technology was transitioned to the infrared astronomical community in relatively short order and was essential to the success of IRAS, COBE and ISO. Mention is made of several of the little known early observational programs that were superseded by more successful efforts.

Measurement and modelling of the directional scattering of light.

Abstract: The quantum nature of light suggests that a photon can interact with matter in two primary ways. Firstly and perhaps more simply, the photon could be absorbed or secondly and more complex, it could be scattered into a new direction of propagation. The scattering process can be thought of as probabilistic, with a statistical distribution of possible new directions of travel with respect to the original. In the case of interaction with a small particle of matter, the probability distribution is referred to as the phase function. In the case of scattering at a surface interface between two bulk materials, the new direction of travel is distributed according to a function called the Bidirectional Scattering Distribution Function (BSDF). The BSDF depends on both the direction of arrival and the direction of scatter (hence bidirectional), the type of material and the condition of the surface as well as the wavelength of light. This work explores a number of areas related to the BSDF, with special attention to the e ects of random light scatter in high performance optical imaging systems such as space telescopes. These demanding imaging applications require optical components manufactured to very high standards with respect to shape, smoothness and cleanliness. This means that random scatter from the surfaces of these optical components must be controlled to very low levels. The measurement of very weak optical surface scatter is therefore a problem of particular interest. An interferometric technique has been proposed here for improving the quality of such measurements. The interference e ects produced in the image by this technique were analysed using Nijboer-Zernike di raction theory, leading to a journal publication in Current Applied Physics.